Computing device for photographic cameras



A ril 1, 1947. A. SIMMON 2,418,370

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 Sheets-Sheet l F/gd FILTER FACTOR DIAPHRAGM 4 REQUIRED 5L LIGHT EXPOSURE I L Ll l LJ -nmrs 46 ACTUAL new FILM SENSITIVITY 1 z 4 a 16 2845.68 H I6225Z Alfred fil'mmon INVENTOR.

ATTORNEY.

April 1, 1947; A. SIMMON 2,413,379

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 SheetS-Shet 2 m mm ' ATTORNEY.

April 1, 1947. snv om 2,418,370

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 Sheets-sheaf. s

A/fi'ed 6/07/770/1 INVENTOR.

I WWW/mm A TTORNEY April 1, 1947. 1 0

CDMPUTINGDEVICE FOR PHOTOGRAPHIC CAMERAS 9 Sheets-Sheet 5 Filed May 25, 1945 A/fifd fiimman IN VEN TOR. Mmih/ M ATTORNEY- April 1, 1947. A. SlMMON 2,413,370

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 Sheets-Sheet 6 :3 we as A/fim fiimmon INVEN TOR.

BY iz/mi Wm ATTORNEK April 1, 1947. SIMMQN 2,418,370

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 Sheets-Sheet 7 7 //&

A/fmd. 5/717/770/7 INVENTOR.

ms/MM ATTORNEY.

April 1, 1947. A. SiM-MON 2,418,370

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 Sheets-Sheet 8 I04- F/ig-i/ D 6/ //07 /O6 64 i g Alfred Sim/770m /97 Z INVENTOR. i Mam m ATTORNEY.

April 1, 1947. A. SlMMON 2,418,370

COMPUTING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed May 25, 1945 9 Shets-Sheet 9 Fly /0 )ilfrfd film/710m INVENTOR.

BY Wm 5 Wm.

ATTORNEY Patented Apr. 1, 1947 COMPUTING DEVICE FOR PHO'IGGRAPHG CAMERAS Alfred Simmon, .lacirson Heights, N. Y., assignor to Simmon Brothers, 1110., Long Island City, N. 2., a corporation of New York Application May 25, 1945, Serial No. 595,702

7 Claims.

The object of this invention is to provide a computing device for photographic purposes, which coordinates the various factors affecting a photographic exposure and indicates the required light intensity which must be reflected by the'scene to be photographed in order to render a correct exposure for a given set of exposure controlling factors. Exposure controlling factors in this sense are the filter factor, the diaphragm ratio of the lens or the so-called F number, the film sensitivity, and the exposure time.

A further object of this invention is to provide a camera with a 'builtin exposure meter and a computing device of this character in operative relation with the meter. Thus the exposure metcr indicates the actual value of the light reflected by the scene to be photographed, the com-- puting device indicates the light required for a given set of exposure controlling factors, and a correct exposure is being obtained whenever the two light values are equal.

In the preferred embodiment of this invention the means to adjust the various exposure controlling factors or" the camer are in operative engagement With'the means to adjust the corre sponding indicators of the computing device so that, for example, the actual setting of the lens diaphragm corresponds to the value indicated by the diaphragm scale of the computing device.

The relations determining the required light intensity are well known and quite simple. The required light intensity increases in direct proportion to the filter factor, if a filter is being used, and it increases with the square of the diaphragm ratio of the lens, the so-called F number. The required light intensity increases in inverse proportion to the film sensitivity and in inverse proportion to the exposure time as determined by the shutter of the camera. The following formula reflects these conditions:

Or in logarithmic terms:

Log L -log C-l-log Fi+1og B -log Slog T As can be noted this formula gives the value of the required light intensity as a function of four variables. In order to coordinate these four variables, numerous devices have been suggested in the past. Usually, some of these values were combined by means of mechanical sliderule-like devices and some or the other values were taken into account by electrical resistors or b means which may be called optical resistors, which decreased the reading of the exposure meter in proportion, or in inverse proportion, as the case may be, to some other magnitudes. Optical resistors in this sense are, for example, grey filters or adjustable diaphragms in front of the photoelectric cell. The objectionable feature of all these resistors is that they reduce the reading.

and therewith thesensitivity of the meterand that very often the meter indications become, therefore, small, diiiicult to read, and inaccurate. Electrical resistors have, furthermore, the disadvantage of getting frequently out of order since they must comprise very many turns of exceedingiy thin wire.

Compared to this prior art, this invention has the advantage that the electric meter is always used at its maximum sensitivity and that always the largest possible movement of the pointer is being observed. It has the further advantage that no mechanical, electrical, or optical connection exists between the meter and the other parts of the camera. ihe computing device itself is quite simple and consistent a relatively small number of parts. It is very compact and, in particular, the final scale indicating required light values does not become longer than the scale of any of the four exposure controlling factors.

In the accompanying drawings,

Fig. 1 illustrates in diagrammatic form the principle of the computing device forming the subject matter of this invention;

Fig. 2 illustrates a more refined form of the device;

Fig. 3 shows a plan view of a camera with a built-in exposure meter and the computing de vice;

Fig. 4. is a front view of the same;

Fig. 5 is a cross sectional View along the plane of line 55 in Fig. 4, the operating levers being shown all in one plane for sake of clarity;

Fig. 6 is a cross sectional View along the plane of line 66 in Fig. 5;

Fig. 7 is a cross sectional view along the plane of line 1-! in Fig. 5;

Fig. 8 is again a front View of the camera but without a protective cover so that certain shafts and levers become visible which actuate the adjustments of the shutter and thediaphragm, respectively;

Fig. 9 is a cross sectional View along the plane 3 of line 9-9 in Fig. 4 showing the computing device as actually incorporated into the camera;

Fig. 10 is substantially the same as Fig. 3, but showing modified means for the setting of the filter factor and the film sensitivity; and

Fig. 11 shows a slight modification of the mechanism used in connection with the camera in accordance with Fig. 10.

Like numbers of references denote similar parts throughout the several views and the following specification.

The principle of the computing device can be best understood with the aid of Fig. 1. Four slides 2|, 22, 23 and 24 are provided which may be moved individually by the operator in either direction. Each of these slides is equipped with a mark 26, 21', 23 and 29, respectively. These marks cooperate with four fixed scales which are calibrated in terms of filter factors, diaphragm ratio or actually the square of the diaphragm ratio, exposure time, and film sensitivity. The lines on these scales are spaced logarithmically, i. e., the distance of any line from the starting point of the scale is proportional to the logarithm of the value indicated by said line. The simplest way to accomplish this, and one which conforms very well with current photographic usage, is to arrange the values on these scales in geometric progression, each line indicating twice the value indicated by the preceding line. Two more slides 3| and 32 are mounted between slides 2| and 22 and slides 23 and 24, respectively. Slide 3| carries a double ended pivoted lever 33, and slide 32 carries an identical pivoted lever 3:1. As can be seen, slide 2| has two projections 35 and 33 form ing a gap engaging one end of lever 33. In an identical manner, slide 22 has two projections 3i and 38 which form another gap engaging the other end of lever 33. The bearings, in which slides 2| and 22 slide, must have a relatively high amount of friction, but the bearings in which slide 3| slides have somewhat less friction. Consequently, if the operator moves, for example, slide 22, slide 2! will remain stationary and the fulcrum of the double ended lever 33, and therewith the entire slide 3|, will move by half the amount of travel of slide 22.

The movements of slides 23 and 24 are coordinated in precisely the same manner and if, for example, the operator chooses to move slide 23, slide 24 will remain stationary and slide 32 will move by half the amount of the movement of slide 23.

Mounted between slides 3i and 32 is a seventh slide 40 which carries the double ended pivoted lever 4|. One end of this lever 4| engages a gap formed by projections attached to slide 3|, and the other end of lever 4i engages a gap formed by projections attached to slide 32. The bearings in which slide 40 slides must have a ver low amount of friction and, consequently, if for example, slide 32 is moved, this movement, in turn, being due to a movement of either slide 23 or 24, slide 40 will move by half the amount of the travel of slide 32 or, if one assumes that the movement of slide 32 was due to a movement of slide 23, the travel of slide 40 will be one-quarter of the travel of slide 23. Slide 40 is equipped with a mark 45, which indicates on scale 45 the required li ht intensity for a correct exposure.

As can be seen, the values of the upper two scales increase from left to right, but the values for the two lower scales increase from right to left. Therefore, an increase in either the filter Movement of I Movement of 1 Movement of Slide 21=log Fi. Slide 3l= 1 Slide 22=log D log F+log D slide 40:

Slide 23=-log T .j Slide 23: Slide 24: log -log Tlo S l In other words, the movement of slide 40 is proportional to the desired function, and the result" scale 46 need not be longer than one quarter of the sum of the four input scales, or approximately as long as any of these input scales. This is very important for compactness and a peculiar advantage of this arrangement. Other devices proposed for this purpose, for example, a flexible ribbon running over a number of pulleys, require an excessively long result scale.

It is most expedient to arrange the scale 46 which indicates the required light intensities, in adjacent arrangement to the exposure meter 50 and provide lines on the exposure meter dial whereby identical light values of scale 46 and exposure meter 53 are bein connected. In this manner, the arrangement immediately indicates to the operator whether the required light intensity is larger, equal, or smaller than the actual light intensity as indicated by the meter. For a correct exposure, the operator has nothing more to do than to adjust at least one of the exposure factors in such a manner that mark 45 and the pointer of the exposure meter 53 are in register.

The mechanical arrangement as shown in Fig. 1, leaves in practice something to be desired since obviously the angle of rotation that can be covered by the pivoted levers 33, 34 and 4| is limited. This, in turn, limits the possible movement of all seven slides and, furthermore, makes the construction of a compact device diflicult if not impossible. A solution which is identical in principle, but more practical becomes possible by considering the two ends of the double ended levers 33, 34 and 4|, respectively, as two diametrically opposed teeth of a primitive gear and by considering in like manner, for example, the projections 35 and 38 attached to slide 2| as two teeth of a rudimentary gear rack. By substituting a complete gear rack for these two projections and by substituting complete gears for the three pivoted levers, one arrives at the design shown in Fig. 2. The four slides 6|, 62, 63 and 64 correspond to the four slides 2|, 22, 23 and 24, respectively. Each has a mark 66, El, E8 and 69 which cooperates with a scale for the filter factor, diaphragm ratio, exposure time and film sensitivity, respectively. Between slide GI and 62 is positioned slide 7| which carries a rotatable gear 63 which is in mesh with the teeth of slides 6| and 62. In like manner, a slide 12 carrying a gear 14 is positioned between slides 63 and 64, gear 14 being in mesh with the teeth of slides 63 and 64. A seventh slide carrying a gear Si is positioned between slides I i "and I2, gearBi being in mesh with the teeth of slides and. I2. Slide 80 is equipped with a mark 85 which indicates on a scale 86the required light intensity. This scale'86 is again in adjacent arrangement to a meter 99 which indicates the actual light conditions, and again a correctly exposed picture will be obtained as soon as the operator brings mark SI and the pointer of meter 90 into register. The movements or the various slides have exactly the same relation to each other as in Fig. 1, i. e., the travel of slide II equals half the sum of the travel of slides SI and 62, the travel of slide i2 equals half the sum of the travel of slides 63 and 64 and finally the travel of slide 80 equals half the sum of the movement of slides II and T2. The scales which indicate the respective position of the four input slides are again arranged in the manner described above, i. e., the values of the upper two scales for the filter factor and the diaphragm ratio, respectively, increase from left to right and the values ofthe two lower scales of the exposure time and film sensitivity, respectively, increase from right to left. Merely as an example, the seven slides are shown to be equipped with elongated slots which engage each two fixed pins thereby permitting a sliding straight line movement of each slide from right to left and vice-versa.

A camera equipped with a computing device built according to this invention is shown in Figs. 3 to 11. In the interest of clarity and simplicity, certain parts of this camera which do not form part of this invention have either been omitted, such as a range and view finder, or they have been shown rather diagrammatically, such as a focusing device of which only the actuating knob or handwheel 99 can be seen.

Camera housing While the camera housing in the drawings has been shown as of one piece construction, it is in reality, of course, suitably sub-divided so as to permit convenient manufacture and assembly. This housing consists essentially of an inner part It'll shaped like a stepped cone forming a light chamber, confining the light rays passing through lens H30 and impinging upon the sensitized photographic film I32, and an outer shell comprising a top Wall I02, a bottom wall I03, a left side wall I03, a right side wall I05, a front wall 05 and a rear wall I01. Underneath the top wall I02, and parallel thereto, is a dividing wall it? which serves to support the various slides of the computing device.

The top wall I02 has a number of elongated slots which are preferably covered by glass or a transparent plastic material and through which the marks associated with the various slides of the computing device are visible. The various scales cooperating with these marks are engraved upon, or otherwise affixed to, the top wall of the camera. The top wall also carries the electrical exposure meter IIO with its pointer III and its dial I I2, see Fig. 3.

The front wall I06 is adapted to receive a shutter H which, together with a camera lens I09, forms, as usual, an integral unit, Figs. 5 and 7. The shutter is, by way of example only, a typical between the lens shutter having a diaphragm adjusting ring and a speed adjusting ring concentrically disposed and coaxial with the camera lens. fwo lugs II 8 and I I9 are fastened to the two rings controlling diaphragm and shutter speed, respectively, and other elements to be described later are vattached"to these lugs.

preferably made from sheet metal, which has a circular aperture for the lens, but which otherwise covers the shutter and its actuating mechanism. Attached to thissafety cover are two guides IZI adapted to receive a filter I22 with its supporting structure I23, Figs. a, 5 and 7. A photo-electric cell I24 which supplies current to the meter I I0 may also be fastened to part I20.

The bottom wall I03 and the right side wall 505 have no noteworthy features and are merely shown for the sake of completeness. Theleft side wall Hit is curved and has four elongated slots permitting the movement of certain levers which'actuate the slides of the computing device and the diaphragm and speed adjustment of the shutter, Figs. 3, l, 5 and 6.

The rear wall is adapted to receive an ,exchangeable roll film magazine I30. This magazine contains two film spools I3l-and a flexible sensitized film I32, which is, during operation, wound from one film spool onto the other in the usual manner. A knob 233 is provided for this purpose. The film magazine also comprises, in reality, a dark slide and means to keep the film as nearly flat as possible, but since these features do not form part of this invention, they have not been shown.

Computing device The computing device as actually incorporated in. the camera can be seen in Figs. '7 and 9. The actual design, as seen in Fig. 9, corresponds very closely to the diagrammatic drawing in Fig. 2 and has, therefore, been assigned the same reference numbers to corresponding parts. The only departure is the shape of the intermediate slides l! and it which are now U-shaped, one leg of the U carrying the gears 13 and ",respectively, and the other leg being equipped with teeth forming gear racks. This obviously does not affect the principle of the computing device, but merely makes a more compact arrangement possible since new gear 3| does not have to be excessively large and since it is now possible to arrange all parts more nearly in one common plane.

M cans to shift slides of computing device In order to enable the operator to shift the slides of the computing device conveniently, an arrangement has been provided for each slide which can best be seen in Fig. 6. It comprises a rotatable lever I52 with a handle which pro trudes through one of the aforementioned elongated slots of the left camera side wall I04, said lever having a lug I42 which, by means of a connecting rod 345 moves another lug I44, which in turn protrudes through an elongated slot in wall Hi8 and is fastened to one of the 4 input slides of the computing device, in this instance, forexample, to slide 62, indicating the diaphragm ratio. Similar arrangements are provided for the other three input slides, as can be seen in Fig, 5, lever I50 actuating the slide for the film sensitivity, lever I5I actuating the slide for the exposure time, and lever I53 actuating the slide for the filter factor. The steps of the above mentioned stepped cone or light chamber serve as pivots for these 4 levers which swivel concentrically with respect to the axis of the camera lens. This concentric arrangement is not strictly necessary, but it is compact and the large bear: ing diameter provides more or less automatically In front of the front wall we is a safety cover I20,

the desired amount of friction in the slide adjustins mechanism.

Means to adjust the lens diaphragm and the shutter speed It is desirable to adjust the actual diaphragm opening of the lens and the actual speed adjustment of the shutter simultaneously with the adjustment of the corresponding slides of the computing device, since otherwise the operator would have to make two adjustments for each of these factors which is not only inconvenient, but-which would make mistakes possible since the operator may not make both adjustments properly at all times. The diaphragm and speed settings usually do not follow any discernible laws and, therefore, cams of suitable configuration must be interposed into the adjusting mechanism at some place in order to provide the necessary corelation. An embodiment of this idea is shown in Figs. 6 and 9. Lever I52 which, as explained above, controls the position of the diaphragm indicating slide 62, carries a cam I60. Sliding on this cam is a cam following roller I6I which is attached to a lever I62. This lever is fastened to a shaft I63 which runs parallel to the lens axis, see Fig. 5. The front end of this shaft penetrates the front wall I06 of the camera. This front end can be seen in Fig. 8 which shows the camera with the safety cover I20 removed. The front end of shaft I63 is fixedly attached to a lever I64 which, by means of connecting rod I65, actuates lug II8 which, in turn, moves the diaphragm adjusting ring of the lens and shutter assembly. A very similar arrangement is used for the speed setting of the shutter. Lever II is equipped with a cam I10, a cross-section of which can be seen in Fig. 5. This cam cooperates with a cam following roller I1I attached to a lever I12 which is not shown but has a shape very similar to that of lever I62. This lever is attached to a shaft I13 parallel to the lens axis and very similar to shaft I63, but longer. Its position with respect to the other parts of the camera can be seen in Figs. 6 and 8. Its front end carries a lever I14 which corresponds to lever I64 of the diaphragm adjusting mechanism, but is arranged in a plane slightly behind it so as to avoid interference. Lever I14 actuates, by means of a connecting rod I15, lug II9 which, in turn, is attached to the speed adjusting ring of the shutter I I5. Two springs I66 and I16 are provided which bias the diaphragm adjusting mechanism and the shutter speed adjusting mechanism, respectively, in such a way that the cam following rollers I6I and I'll are always in contact with their respective cams I50 and I10.

Means to coordinate film factor and film sensitivity To make the camera as foolproof as possible, it is desirable to provide means to facilitate the correct adjustment of the slides for the filter factor and the film sensitivity, respectively. Referring to Fig. 4, it will be noted that the filter I22 is carried by a filter mount I23, which in turn can be inserted into the grooves of the two filter guides I2I as described above. The upper end of this filter mount carries an abutment I80 which shows a legend describing the filter and a fixed mark which, when the filter is properly inserted into the camera, shows on the filter factor scale on top of the camera the proper numerical filter factor for this filter. The operator then merely moves lever I53 until the mark of the filter factor slide of the computing device and the mark on the abutment I60 of the filter mount are in register as shown in Fig. 3.

On top of the camera itself, opposite the first line of the filter factor scale, is a similar mark which is not visible as soon as any filter is inserted into the camera, but becomes visible whenever the camera is being used without any filter. This mark is shown in dotted lines in Fig. 3. This reminds the operator to move lever I53 back until the movable mark of the filter factor indicating slide also points to the first line. In other words, both visible marks must, at all times, be in register.

Similar means are provided for the convenient adjustment of the computing device for various film sensitivities. The exchangeable roll film magazine I30 carries a nameplate with a mark, describing the film with which this magazine is loaded. When the roll film magazine is inserted into the camera this nameplate with its mark is in adjacent arrangement to the film sensitivity scale on top of the camera and the mark points at that line of the scale which corresponds to the film sensitivity of the film in the magazine. The operator then moves lever I50 until the sliding mark of the film sensitivity slide of the computing device is in register with the fixed mark on top of the roll film magazine.

The entire arrangement can be seen in Fig. 3. It is simple; it provides the operator, at a glance, with all pertinent information on th adjustments of the camera, and the juxtaposition of the two respective marks for the filter factor and the film sensitivity is a very effective and substantially foolproof reminder for the operator. However, a still more nearly foolproof arrangement can be made and is shown in Fig. 10 which shows a plan view of a camera, very similar to Fig. 3 except for certain modifications which are about to b described. Instead of mark 66 indicating the filter factor scale, there is an actual projection I90 protruding through the elongated slot in the top wall of the camera housing. This slot is, of course, no longer closed by a transparent window. A similar projection I9I is provided on the abutment I of the filter mount I22. The filter factor indicating slide is biased by a spring I92 which is shown in Fig, 11 and has, therefore, the tendency to return automatically to the lowest settling on this filter factor scale, i. e., to line #1, and it will assume this position in the absence of a filter. However, should the operator decide to use a filter, he merely moves the projection I as far to the right as necessary, by lifting handle I53, inserts the filter mount and releases handle I53, whereupon projection I90 will automatically move back until it meets the projection l9I on the filter mount. Projection I90 has a shape which will not permit the correct insertion of the filter mount into the camera unless the operator proceeds in the manner described.

An identical arrangement can be provided for the automatic adjustment of the film sensitivity slide 64 of the computing device. This slide 64 is now, instead of a mere mark 69, equipped with an actual projection I 95 which protrudes through the elongated slot on top of the camera housing and which cooperates with a similar mark I96 fastened to the exchangeable roll film magazine I30. The slide 64 is again biased by a spring I91, shown in Fig. 11. The operator again proceeds by first shifting slide 64 with its projection I95 sumciently far towards the right, whereupon he insertsthe'roll film magazine and releases handle I50. Spring l9? then will cause slide 64 with its projection I85 to return until projection I95 meets projection 355. In other words, the film sensitivity slide of. the computing device will in this manner automatically assume the correct position. The mark which is affixed to the roll film magazine, is shaped in such a manner that correct insertion of the magazine is not possible unless the operator shifts mark I95 first in the describedrnanner.

Sometimes, particularly in the case of relatively inexpensive cameras, it may be advisable to keep the appearance of the camera as simple as possible. In this case, the two scales for the filter factor and film sensitivity may be omitted, and merely the coacting projections it!) and HM, and I95 and I 35, may be provided. The proper adjustment of the computing device is automatically assured by this interlocking arrangement, and the operator is very often not interested in the exact numerical values of filter factor and film sensitivity, so long a correct exposure are being obtained.

The operation or the camera and the coaction of the various parts can now be fully understood from the description above. Depending upon the type of picture which the operator plans to take, he selects a film magazine loaded with a suitable type of film and inserts it into the camera. If the camera is equipped with an interlocking arrangement, such as shown in Fig. 10, the film sensitivity slide of the computing device will automaticah ly be in the correct position after insertion of the magazine. With the arrangement of Fig. 3 the operator moves lever Hill until mark G9.- is register with the corresponding mark on the film magazine. The operator then decides whether a filter may advantageously be used and, if necessary, selects a suitable on and inserts it into the camera. With an interlocking arrangement such as shown in Fig. 10, the filter. factor slide of the computing device assumes automatically the correct position. With a device such as shown in 3,the operator moves handle 53 until mark 66 is in register with the corresponding mark on the filter mount.

The next step is to adjust the exposure time of the shutter and of the computing device by movhandle I51. time depends upon a number of factors, but more than anything else, upon the speed with which the object to be photographed moves. It is usually auvantageous to choose the longest possible eXposure time compatible with the speed of a moving object because this permits the use of the smallest possible diaphragm stop, thereby assuring the best possible depths of focus.

The camera. is then pointed at the scene to be photographed, usually with the aid of a view finder which, however, as explained above, is not shown on the drawings. Light reflected by the scene impinges upon the photo-electric cell E24 and causes it to generate an electrical current which is measured by'the meter 5 i ii on top of the camera. 'The pointer I i may, for example, assume the position shown in 3. Ihe operator then adjusts the diaphragm, and the diaphragm slide of the computing device, by moving handle l-Ell until mark 235 is in regiszer the pointer l i i of the indicating meter. This indicates that all factors have been chosen in such a way that the required light value, as computed by the computing device, equals the actual light value as measured by the The most favorable exposure 10 g, exposur meter. The camera is now ready for a correctly exposed picture.

An experienced operator will usually choose his factors in such a way that, by merely moving the diaphragm setting, mark can be brought into register with the meter pointer without difiiculty. Under certain circumstances, however, this may be impossible; for example, an inexperienced operator may choose a slow film, a dense filter, and a short exposure time under unfavorable light conditions and then, even with the diaphragm wide open, the required light intensity may still be larger than the actual intensity as indicated by the meter. In other words, mark 85 will be to the right of pointer Ill. This means that no correctly exposed picture is possible under the circumstances and the operator has to change some of the exposure controlling factors. Usually it is most convenient to use a longer exposure time, but should this not be sufficient, the. operator has to use a faster film, or a less dense filter, or omit the filter altogether.

In the same manner, the operator may choose inadvertently a very fast film, no filter, and a relatively long exposure time under extremely bright light conditions, for example, at the seashore in bright sunlight. It is possible that under these conditions the actual light intensity may consistently be higher than the required intensity so that over-exposure would result. This is immediately indicated by the fact that mark 85' cannot be brought in register with. point III, but remains always to the left of it. Again, some exposure factors would have to be changed; for ex ample, a higher shutter speed may have to/be chosen. Since, under ordinary conditions, the adjustment of the diaphragm will be made last, i. e., almost immediately before the actual exposure, a larger and more conspicuous handle I52 has been provided for this purpose.

I wish to emphasize that this description covers merely a preferred embodiment of the invention, and that many details may be freely changed without departing from its spirit. For example, while I have consistently shown stationary or fixed scales attached to the camera housin and movable marks attached to the various slides of the computing device, this arrangement may very well be reversed, i. e., the scales may be attached to the slides and stationary marks may be afiixed to the camera housing. It has already been menticned that for the purpose of this invention the two ended pivoted levers, such as shown in Fig. 1, may be considered the mechanical equivalent of gears, and that a slide equipped with two projections forming a. gap between themselves may be considered the mechanical equivalent of agear rack. The cam and lever arrangement illustrated in Fig. 6 may also be reversed. Asshown, the slides of the computing device, for example, slide fiLFig. 6, are actuated through connecting rods M3 by lugs Hi2 afiixed to the adjustin levers, for example, I52, and the levers adjusting the. diaphragm ltd and the shutter speed I14, respectively, are actuated by cams I50 and I'll], also afiixed to said levers. Obviously, the opposite arrangement, i. e., the actuation of the computer slides by cams and the actuation of the dia phragm' and speed adjusting mechanism by connecting links, is the obvious mechanical equivalent of the arrangement shown and should be con strued to fall within the scope of this invention. The means to actuate the slides of the computing device do not necessarily have to be constructed in the manner shown and, particularly, the ac- 11 tuating levers I50, li, I52 and i53 do not have to rotate on bearings which are concentric with the lens axis. While I have shown an exchangeable roll film magazine, it will be obvious that a magazine containin any other type of sensitized material such as cut or pack films would be equally applicable. Variations of this character and obvious mechanical equivalents of this type shall be construed to be covered by the appended claims.

What I claim as new is:

1. A camera comprising a housing, filter supporting means in the housing, a lens with a diaphragm, a shutter, light sensitive film supported within the housing, a photoelectric cell and a current measuring instrument connected to said cell, said instrument equipped with a movable pointer and a scale calibrated in light values for indicating the actual intensity of the light refiected by the scene to be photographed, a device to compute the light intensity required for a correctly exposed picture from a given set of values for the filter factor, diaphragm opening, shutter controlled exposure time and film sensitivity, respectively, said device comprising a supporting structure attached to the camera housing and four slides, said slides movable in-- dividually and independently along straight and parallel lines, each of said slides having a mark, a stationary scale on said structure for each of said slides and cooperating with the marl: or" its slide, the first of said scales calibrated in logarithmically spaced values O L filter factors, the second of said scales calibrated in values of the ratio of the focal length of the camera lens divided by the effective diaphragm diameter of said lens, the spacing of said values being in proportion to the logarithms of their squares, the indicated values of both scales increasing in the same direction, the third of said scales calibrated in logarithmically spaced values of the exposure time of the shutter of said camera, and the fourth of said scales calibrated in logarithmically spaced values of the film sensitivity, the indicated values of said last two scales increasing in the opposite direction to that of the first two scales, each of said slides equipped with a gear rack, the racks of one pair of slides facing each other, and the racks of the other pair of slides facing each other, a gear between the racks of the first pair and in mesh with both, a fifth slide, said gear mounted rotatably upon said fifth slide, a second gear between the racks of the second pair and in mesh with both, a ixth slide, said second gear mounted rotatably upon said sixth slide, said fifth and sixth slides movable along straight lines parallel to the lines of movement of the first four slides, and each equipped with a gear rack, said racks facing each other, a third gear between the racks of said fifth and sixth slides and in mesh with both, a seventh slide, said third gear mounted rotatably upon said seventh slide, said seventh slide movable along a straight line parallel to the lines of movement of all other slides, and a mark on said seventh slide cooperating with a stationary scale on said structure calibrated in logarithmically spaced values of required light intensities, said last mentioned scale adjacent to the scale of said instrument and lines connecting identical light values on both scales, a correctly exposed picture being assured whenever the last mentioned mark indicates the same light value as the pointer of said instrument thereby making the "required" light value equal to the actual value of the light reflected by the scene to be photographed, and mechanism interconnecting said computing device with exposure adjusting means of the camera.

2. A camera, according to claim 1, said mechanism including means to adjust the diaphragm of the camera lens and the slide cooperating with said second mentioned scale of the comput ing device simultaneously so that the actual value of the diaphragm ratio is the same as the value indicated by the mark associated with said slide.

3. A camera, according to claim 1, said mechanism including means to adjust the shutter controlled exposure time and the slide cooperating with said third mentioned scale of the computing device simultaneously so that the actual value of the exposure time is the same as the value indicated by the mark associated with said slide.

4. A camera, according to claim 1, a filter carried by said filter supporting means and being mounted in a filter holder carrying a mark, said mark, when the filter holder is positioned in front of the camera lens, indicating on said first mentioned scale the correct numerical filter factor for said filter.

5. A camera, according to claim 1, said camera equipped with an exchangeable film magazine, a mark affixed to said magazine, said mark, when the magazine is in operative connection with the camera indicating on said fourth mentioned scale the sensitivity of the film in said magazine.

6. A camera, according to claim 1, the slide cooperating with said first mentioned scale of the computing device having a projection, and a spring urging said slide towards the position of lowest filter factor, a filter carried by said filter supporting means and being mounted in a filter holder carrying another projection adapted to restrain said first mentioned projection when the position of the slide cooperating with said first mentioned slide is in accordance with the value of the filter factor of said filter.

i. A camera, according to claim 1, the slide cooperating with said fourth mentioned scale of th computing device having a projection, and a spring urging said slide towards one extreme position, said camera equipped with an exchangeable film magazine having another projection adapted to restrain said first mentioned projection when the position of the slide cooperating with said fourth slide is in accordance with the value of the film sensitivity of th film in said magazine.

ALFRED SIMMON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,864,180 Bing June 21, 1932 2,213,642 Tonnies Sept. 3, 1940 2,340,622 Simmon Feb. 2, 1944 

